High resolution differential mode delay measurements and bandwidth of multimode fibers

Summary form only given. There is growing interest in the use of multimode fibers for high speed data networks. According to present industry test procedures, multimode fiber bandwidth is characterized using overfilled launching conditions. Such a launch is achieved by uniformly exciting the core and launching with a numerical aperture (NA) which exceeds the fiber NA. For many multimode fibers, the bandwidth increases when the launching conditions are restricted; the specific behavior, however, depends on the differential mode delay (DMD) characteristics of the refractive index profile. We have developed a frequency domain phase shift technique capable of acquiring DMD profiles with a temporal resolution less than 0.2 ps. DMD measurements are now possible on fiber lengths as short as 15 m